I recall a few DE's that were 6'5", but none that were over that...
The Baccus brothers in the 1970's.
Bruce Deloney 1971
Joel Estes 1974-75 was 6'6" and came to OU as a linebacker. Was tried at DT. Highly recruited but he never panned out.
Dan Cody 2000-04
David King 2008-12
Geneo Grissom 2010-14, also played LB
6'7" sounds intimidating for any player, especially a DE, but don't see it being a big factor necessarily......unless overall aptitude is present.
It's the same with linebackers. I think too much importance is given to height at that position, but it appears that Grinch prefers his linebackers at or over 6'2" according to OU's last two recruiting hauls.